1. Field of the Invention
The present invention relates to an apparatus for focusing a light beam onto an information memory medium, and more particularly, to an apparatus which prevents a destruction of the data recorded on the medium, during initial operation.
2. Description of the Related Art
Optical disks are classified into two types. The first type is called a write-once disk, and the second type is called an erasable disk. Data is recorded on either type of an optical disk by means of a data recording apparatus which has an optical head including, for example, a semiconductor laser, and an objective lens. More specifically, the laser beam which the semiconductor laser emits is applied to the optical disk, thereby recording the data thereon.
The optical head must not be turned on to cause the laser to emit a laser beam, before the following conditions are checked and confirmed:
1. The cover of the data recording apparatus is closed, preventing the laser beam from leaking from the apparatus to harm the operator of the apparatus.
2. The optical disk is placed at the prescribed position within the data recording apparatus.
3. The optical disk is spinning at a predetermined speed.
After all these conditions have been confirmed, the optical head is turned on to emit a laser beam, and the focus servo unit is operated, thus driving the objective lens so as to focus the laser beam on the optical disk correctly. When the initial-phase operation, such as the driving of the objective lens for focusing the beam, is started, it is not ascertained where the optical head is located with respect to the optical disk. Thus, the objective lens is driven, whether or not the optical head faces the data-recording region of the optical disk. Hence, if the lens faces the datarecording region, and if the focus servo unit fails to function appropriately, the objective lens will collide with the data recording region of the optical disk, inevitably destroying the data recorded on the disk.
The data recorded on the optical disk may be destroyed by another cause. As is known, a laser beam of a relatively low intensity is applied to the disk, either the write-once type or the erasable type, to reproduce data therefrom, and a laser beam of a relatively high intensity is applied to the disk to record the data thereon. If the laser emits an intense beam by accident while the optical head is facing the data-recording region of the disk in the initial operation phase of the head, this beam will destroy the data recorded on the part of the disk which it illuminates and which must be saved. Unless the laser is immediately turned off, it continues to emit the intense beam onto the data-recording region, inevitably destroying more and more data as the disk spins.